It's unlikely tiles will "buckle" however the underlayment is likely the
problem. Likely those tiles are not on concrete but something more prone
to shrinking and swelling.

I was wondering about that because of something I was just watching on
HGTV (I admit it). They were talking about the backerboard they were
going to us.

I think the only way to solve this is to pull them up to see what's
there. If we buy it, we'll do that anyway. Even in our house where
we live now we have painted concrete floors and I think that would be
ideal at a lake house.

Thanks, folks!

Brad